1. Field of the Invention
This invention relates to precision butting of semiconductive chips, and more particularly to an improved fabrication process for large array image sensors or thermal ink jet printheads, wherein sectioning of semiconductive wafers containing the sets of image sensors or heating element arrays to produce sub-units for assembly into pagewidth lengths include cutting two separate parallel lines in opposite directions by an angled dicing blade to produce kerfs with equal but opposite slopes.
2. Description of the Prior Art
Fabrication of pagewidth silicon devices, such as image sensor arrays having photosites and supporting circuity integrated onto a silicon substrate and thermal ink jet printheads having an etched silicon structure mated and bonded to a silicon substrate with heating elements and addressing electrodes, impose economically difficult fabricating processes on manufacturers because of the close tolerance requirement for the abutting edges of side-by-side sub-units assembled to produce the pagewidth devices. For although the standard technique of dicing or scribing and cleaving silicon wafers used by the semiconductive industry produces silicon devices or chips having reasonably controlled dimensions, the microscopic damage occurring to the chip surface during the scribing or dicing operation has effectively precluded the deposition of circuitry or photosites at the chip edge. This has necessitated that a safe distance be maintained between the last circuit element or photosite and chip edges, if operation of these adjacent photosites or ink jet circuitry is not to be impaired by the presence of either microcracks or silicon chipping along the cleaved or diced edges.
U.S. Pat. No. 4,604,161 to Araghi addressed this problem. Araghi discloses the concept of chemically etching a V-groove in the surface of a wafer followed by a partial cut in the back of the wafer forming an inside groove directly underneath the V-groove. This allows the dies to be separated from one another by means of a mechanical cleaving or breaking operation. In this approach, the cut through the top surface of the wafer, in which the active elements are built, was not made with an abrasive blade but by means of the chemically etched V-groove. As a result, the propagation of mechanical damage along the top surface of the wafer was avoided, allowing active elements to be placed as close to the V-groove as the accuracy of the photolithography and the etching operation would allow.
However, the Araghi technique leaves at least one face of the cleaved chip with a protruding knife edge defined by two intersecting {111} planes. This knife edge can be very delicate and easily damaged. Such damage may require that the chip be rejected, reducing fabrication yields and increasing cost.
Copending and commonly assigned patent application Ser. No. 090,827, filed Aug. 28, 1987, entitled "Method of Fabricating Image Sensor Dies For Use in Assembly Arrays", to Jedlicka et al, seeks to address and rectify the above by providing a method of fabricating high resolution image sensor dies from a silicon wafer so that the dies have precision vertical faces to enable the dies to be assembled with other like dies to form a larger array without image loss or distortion at the points where the dies are assembled together. Small V-shaped grooves are etched in one side of a (100) silicon wafer delineating the faces of the chips where the chips are to be separated from the wafer with the walls of the V-shaped grooves being parallel to the {111} crystalline planes of the wafer. Wide grooves are formed in the opposite side of the wafer opposite each of the V-shaped grooves with the axis of the wide grooves being parallel to the axis of the V-shaped groove opposite thereto. In the final process step, the wafer is sawed along the V-shaped grooves with one side of the cut made by the sawing being substantially coextensive with the bottom of the V-shaped grooves and perpendicular to the wafer surface. Accordingly, one side of the V-shaped grooves is obliterated by the sawing, and the sides of the V-shaped grooves that remain serve to prevent development of fractures in the die beyond the remaining side, as the wafer is sawed.
Thermal ink jet printing systems use thermal energy selectively produced by resistors located in capillary filled ink channels near channel terminating nozzles or orifices to vaporize momentarily the ink and form bubbles on demand. Each temporary bubble expels an ink droplet and propels it towards a recording medium. The printing system may be incorporated in either a carriage type printer or a pagewidth type printer. The carriage type printer generally has a relatively small printhead, containing the ink channels and nozzles. The printhead is usually sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is reciprocated to print one swath of information at a time on a stationarily held recording medium, such as paper. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath, so that the next printed swath will be contiguous therewith. The procedure is repeated until the entire page is printed. For an example of a cartridge type printer, refer to U.S. Pat. No. 4,571,599 to Rezanka. In contrast, the pagewidth printer has a stationary printhead having a length equal to or greater than the width of the paper. The paper is continually moved past the pagewidth printhead in a direction normal to the printhead length and at a constant speed during the printing process. Refer to U.S. pat. No. 4,463,359 to Ayata et al for an example of pagewidth printing and especially FIGS. 17 and 20 therein.
U.S. Pat. No. 4,463,359 mentioned above discloses a printhead having one or more ink filled channels which are replenished by capillary action. A meniscus is formed at each nozzle to prevent ink from weeping therefrom. A resistor or heater is located in each channel upstream from the nozzles. Current pulses representative of data signals are applied to the resistors to momentarily vaporize the ink in contact therewith and form a bubble for each current pulse. Ink droplets are expelled from each nozzle by the growth of the bubbles which causes a quantity of ink to bulge from the nozzle and break off into a droplet at the beginning of the bubble collapse. The current pulses are shaped to prevent the meniscus from breaking up and receding too far into the channels, after each droplet is expelled. Various embodiments of linear arrays of thermal ink jet devices are shown, such as those having staggered linear arrays attached to the top and bottom of a heat sinking substrate for the purpose of obtaining a pagewidth printhead. Such arrangements may also be used for different colored inks to enable multi-colored printing.
U.S. Pat. No. Re. 32,572 to Hawkins et al discloses a thermal ink jet printhead and method of fabrication. In this case, a plurality of printheads may be concurrently fabricated by forming a plurality of sets of heating elements with their individual addressing electrodes on one substrate, generally a silicon wafer, and etching corresponding sets of channel grooves with a common recess for each set of grooves in another silicon wafer. The wafer and substrate are aligned and bonded together so that each channel has a heating element. The individual printheads are obtained by milling away the unwanted silicon material to expose the addressing electrode terminals and then dicing the substrate to form separate printheads.
U.S. Pat. No. 4,638,337 to Torpey et al discloses an improved printhead of the type disclosed in the patent to Hawkins et al wherein the bubble generating resistors are located in recesses to prevent lateral movement of the bubbles through the nozzles and thus preventing sudden release of vaporized ink to the atmosphere.
U.S. Pat. No. 4,678,529 to Drake et al discloses a method of bonding the ink jet printhead channel plate and heater plates together by a process which provides the desired uniform thickness of adhesive on the mating surfaces and prevents the flow of adhesive into the fluid passageways.
U.S. Pat. No. 4,612,554 to Poleshuk discloses an ink jet printhead composed of two identical parts, each having a set of parallel V-grooves anisotropically etched therein. The lands between the grooves each contain a heating element and its associated addressing electrodes. The grooved parts permit face-to-face mating, so that they are automatically self-aligned by the intermeshing of the lands containing the heating elements and electrodes of one part with the grooves of the other parts. A pagewidth printhead is produced by offsetting the first two mated parts, so that subsequently added parts abut each other and yet continue to be self-aligned.
U.S. Pat. No. 4,774,530 to Hawkins, discloses the use of an etched thick film insulative layer to provide the flow path between the ink channels and the manifold, and copending and commonly assigned patent application Ser. No. 126,085, filed Nov. 27, 1987, entitled "Thermal Ink Jet Printhead and Fabrication Method Therefor" to Campanelli et al, discloses the use of an etched thick film insulative layer between mated and bonded substrates. One substrate has a plurality of heating element arrays and addressing electrodes formed on the surface thereof and the other being a silicon wafer having a plurality of etched manifolds, with each manifold having a set of ink channels. The etched thick film layer provides a clearance space above each set of contact pads of the addressing electrodes to enable the removal of the unwanted silicon material of the wafer by dicing without the need for etched recesses therein. The individual printheads are produced subsequently by dicing the substrate having the heating element arrays.
Copending and commonly assigned patent application Ser. No. 137,283, filed Dec. 23, 1987, entitled "Large Array Thermal Ink Jet Printhead", to Drake et al, discloses a large array ink jet printhead having two basic parts, one containing an array of heating elements and addressing electrodes on the surface thereof, and the other containing the liquid ink handling system. At least the part containing the ink handling system is silicon and is assembled from generally identical sub-units aligned and bonded side-by-side on the part surface having the heating element array. Each channel plate sub-unit has an etched manifold with means for supplying ink thereto and a plurality of parallel ink channel grooves open on one end and communicating with the manifold at the other. The surfaces of the channel plate sub-units contacting each other are {111} planes formed by anisotropic etching. The channel plate sub-units appear to have a parallelogram shape when viewed from a direction parallel with and confronting the ink channel groove open ends. The heating element array containing part may also be assembled from etched silicon sub-units with their abutting surfaces being {111} planes. In another embodiment, a plurality of channel plate sub-units are anisotropically etched in a silicon wafer and a plurality of heating element sub-units are formed on another silicon wafer. The heating element wafer is also anisotropically etched with elongated slots. The wafers are aligned and bonded together, then diced into complete printhead sub-units which have abutting side surfaces that are {111} planes for accurate side-by-side assembly.
Drop-on-demand thermal ink jet printheads discussed in the above patents and pending applications are fabricated by using silicon wafers and processing technology to make multiple small heater plates and channel plates. This works extremely well for small printheads. However, for large array or pagewidth printheads, a monolithic array of ink channels or heating element arrays cannot be practically fabricated in a single wafer.
The fabrication approaches for making either large array or pagewidth thermal ink jet printheads can be divided into basically two broad categories; namely, monolithic approaches in which one or both of the printhead components (heater substrate and channel plate substrate) are a single large array or pagewidth size, or sub-unit approaches in which smaller sub-units are combined to form the larger array or pagewidth print bar. For examples of the sub-unit approach, refer to the above-mentioned U.S. Pat. No. 4,512,554 to Poleshuk, and in particular to FIG. 7 thereof, or the pending application Ser. No. 137,283 to Drake et al. The sub-units approach may give a much higher yield of usable sub-units, if they can be precisely aligned with respect to each other. The assembly of a plurality of sub-units, however, require precise individual registration in both the x-y-z planes as well as the angular registration within these planes. The alignment problems for these separate units presents quite a formidable task, the prior art solution of which makes this type of large array very expensive.